Read as much as you can about guinea-pigs. They are fantastic but in their own way quite complex little animals.
They like routine and kind words (they don't mind what you say as long as the tone is kind), especially if the kind words are "Here's your supper pigs" 
They need protected against everything . Cold, heat, damp, predators.
They are quite vunerable really. They like to run up to your neck and snuggle their. Ours are good at letting us know they need a pee but my pig GP8 just sat lifting her rump and leaving me a pile of droppings !
In return you'll get chatty ( noisy ) endearing little pets.
Read up on their food, they eat fairly constantly and cannot vomit.
There are loads in Rescue, lots of boars in pairs . Boars are lovely cuddly pigs but need loads of space.
They flipping well break your heart when they die, they do have a tendancy to go quite quick. Often you'll find them dead in the cage when the night before they were ok. Or they do that starey coat tucked up look which bodes that they're on the way to The Bridge.
We've cuddled guineas in their final hours, had them go in the Pighouse and had to have one PTS. Even though you know you've done your best for them its hard to lose them.
They gouge a space in your heart and burrow their way in .